Optical prism system



'Nov. 5, 1946. STREET OPTICAL PRISM SYSTEM Filed Dec. 15, 1945 DONALDT.STREET l'mventor Gttorneg UNITED STATES Patented Nov. 5, 1946 PATENTOFFICE OPTICAL PRISM SYSTEM Donald T. Street, Rochester, N. Y., assignorto Bausch & Lomb Optical Company, Rochester, N. Y., a corporation of NewYork Application December 15, 1945, Serial No. 635,176

Claims.

This'invention relates to optical instruments and more particularly toprismatic instruments I and a. prismatic reversing system therefor.

Prismatic reversing systems are generally employed in binocularinstruments to deviate the lightrays to cause a reversal of the imageinverted by an objective so that the image of the object 1' will appearerect and magnified to the eye of the observer. These systems alsocompact the path ,of the light rays in the instrument and thereby reducethe (without; sacrificing the advantages realized by a I relatively longoptical path.

dimensions of the instrument -Heretofore,prismatic reversing systemshave .usually-comprised-at least four prisms with two --or.;more of theprisms cemented to each other or the-prisms have been held in spacedrelation to .eachotherinthe instrument. Cemented prisms ,areobjectionable; in that, the activefaces of the prisms are difificulttoaccurately locate relative 'to each other in the cementing operation tosecure .their correct optical performance. Also, the

formation of cement' blisters between the located faces and thedifiiculty of maintaining the cement free from dust have furthercomplicated this expensive operation. Where the prisms are heldseparated within the instrument, the many glassto-air surfaces of theprisms reduce the brilliancy of the light by light losses and must beaccurately ground and-finishedto prevent distortion of the image. 7

It has been suggested to form two or more of these prisms as an integralunit to reduce the number of glass-to-air surfaces, but the expense ofaccurately finishing a unitary prism with a large number of opticallyfiat faces related to each other by angles having very small tolerancelimits has been prohibitive to the economical manu- Whether the.

prisms be cemented orheld separated within the facture of opticalinstruments.

instrument, considerable difiiculty has been had in mounting the prismsin the instrument due to the shape of the prisms which required the useofstraps, springs, or the like, to hold them within the instrument sothat the prisms remained permanently in correct optical alignment.

1 The principal object of the present invention is to obviate thesedifliculties and disadvantages had in optical instruments employingprior prismatic reversing systems by providing a prism reversingsystemior optical instruments, and more especially binocularinstruments, comprising two roof prisms of the'Amici' type havingmutually cooperating reflecting 'faces causing a reversal of theima'ges'intheir passages through the prism (01. ss 3s 10 when mounted in abinocular instrument. This permits a substantial saving to be effectedin the cost of these instruments.

Also, the correct optical alignment of the prisms in the instrument maybe readily secured, for it is only necessaryto position the two prismsin the instrument in opposed relationshipwith the roof faces of theprisms outwardly disposed relative to each other and the other faces ofthe prisms inwardly disposed in spaced relation to each other. Theaccurate positioning and mounting of the prisms is further facilitatedfor, after thus positioning and holding the prisms, the triangularsidesof the prisms may be cemented to the inner walls of a flat andhollow mounting body which may be die-cast or otherwise readily formed.

By thus locating and. mounting the prisms, the prisms are rigidly heldin correct and permanent optical alignment within the instrument body.'As the prisms may be readily mounted in 'the instrument and theinstrument body is easily formed, substantial savings are furthereffected in the manufacturing costs of optical instruments.

Other objects and advantages of the present invention will appear fromthe following description taken in connection with the accompanyingdrawing, in which:

Fig. 1 is a perspective view of the prismatic reversing system of thepresent invention. Fig. 2 is a diagrammatic View of a binoculartelescope constructed in accordance with my invention.

Fig. 3 is a diagrammatic view of a binocular microscope constructed inaccordance with my invention.

Fig. 4 is a diagrammatic view of a modified binocular microscopeconstructed in accordance with my invention.

This application is a continuation-in-part of my co-pending application,Serial No. 511,978 filed November 27, 1943.

The prismatic reversing system of the present invention, as illustratedin the drawing and more particularly in Fig. 1, comprises two opposedroof prisms l0 and II of the Amici type with the respective roofs l2 andl3 of the prisms outwardly 2-5 disposed and the lower inner or entrancefaces I4 and the upper inner or exit faces I 5 of the prisms angularlydisposed to each other, the substantially triangular sides It and i? ofeach prism being parallel to each other. v

Each of the prisms is made from a single block of glass and apart fromthe roof faces, has only two optically flat faces, which are theentrance face i4 and the exit face I5. The prisms are similarly formedwith the faces I4 and I5 of each prism angularly disposed to the roofedge and 120 to each other. The roof faces I8 and I9 bf each prism areat right angles to each other and therefore angularly disposed at anangle of 90. Coatings of reflecting material, such as distilled rhodiumor aluminum, are deposited on portions of the surfaces M and I5 as shownat I4 and I5. Such layers are opaque and extend over approximately thelower two-thirds of surface I4 and upper two-thirds of surface l 5 sothat the reflecting layers do not interfere with the passage of lightrays through the other portions of surfaces I4- and I5.

In'the position of the prisms it and II shown in perspective in Fig.1,-the roof edges are parallel to each other and therefore a beam oflight, indicated by a dot-dash line and parallel to the roof edge of theprism it, is reflected by the reflecting layer M on plane face it of theprism II! to the prism I i. The beam of light passes normal to andthrough the plane face 'I f the prism I land is twice reflected by theroof faces I8 and I9 of this prism. As the beam is reflected from theroof of the prism I l normal to the plane reflectingf'ace 'I5of theprism I I, it passes therethrough and :is angularly deviated by thereflecting layer I5' on plane face l5 of the prism Eil to emerge inalignment with the path of the entering beam.

In like manner, the beam angularly incident on thereflecting layer M onface I4 of the prism I Ifis reflected through the face'l5 of the prismI0 "tojt he roof of the prism Iii. The roof of the prism to twicereflects the beam and itpasses through'the face I5 of the prism I Eltothe'reflect- 'ingla'yer on face I5 of the prism "Il. As the face SIB,oftnepri'sm l I is angularly disposed sufficientlyto reflectthebeam,'the' beam is reflected and femerges'inalignment with its path ofentrance. "It can now be seen that the mutuallycooperative reflectingfaces of the prism system will deviate "each beam of lightincident onthe entrance faces "I4 and emergent 'from'the exit faces I5 of theprisms by four reflections to cause the images to be'completelyreversed-as shown in Fig. 1.

Referring to Fig. 2, there is diagrammatically shown the prismaticreversing system of the present invention embodied in a binoculartelescope, wherein the prisms I0 and H are disposed between theobjectives 2i and 22 and the oculars '23 and 24. It will be readilyapparent that the prismatic reversing system will cause a beamof lightaxially entering the objective ZI parallel to the roof edge "of theprism IE! to be reflected by the prism It] to the prism II and thenreflected by the prism I-I back to the prism I0 to emerge therefromaxially of the ocular 23.

Also, the beam of light axially entering the objective 'ZI is similarlyreflected by the prisms I0 and I! to emerge therefrom axially of theocular 24.

In this manner, by the interaction of the prisms,the images formed bythe objectives will be completely reversed upon emergence from theprismatic reversing'system. The length ofthe optical path of each beamin the system permits objectives of 'long'focal length'tobe usedtoinsure a highdetion of the reflecting faces of the prisms, the

prisms may be readily mounted in a single flat and hollow instrumentbody for the triangular sides of the prisms may be cemented to the innerwalls of the body. Also, the flat and compact body of the instrumentpermits the convenient use and ready handling of the instrument and theinstrument is pleasing in appearance.

In Fig. 3, there is diagrammatically shown the prismatic reversingsystem of the present invention embodied in a binocular microscopewherein iii and H indicate the prisms disposed between the oculars 25and 23 and the objectives 2! and 28 of the microscope. Each of theobjectives 2! and 28 are angularly disposed to each other to focus on anobject held by a suitable stage (not shown). To deviate the respectivebeams shown as axially traversing the objectives so that the emergentbeams will issue axially of the angularly inclined oculars 2 5 and 26,the prisms III and II have their roof edges angularly inclined to eachother to reduce the angle subtended by the lower inner faces of theprisms and enlarge the angle subtended by the upper inner faces of theprisms. By thus positioning the prisms,the respective diverging beams oflight axially traversing the objectives if and 28 will strike the lowerreflecting faces of these prisms and be reflected by the prism system todivergingly emerge from the upper reflecting faces of the prisms in therespective axes ofthe'angularly disposed oculars25 and'26. The imagesformed by the beams of light traversing the objectives will-be reversedby the prism system and-will pass'to the oculars 25 and 26.

Referring to Fig. 4, there is diagrammatically shown a modification ofthe prismatic reversing system of the present invention embodied in abinocular microscope wherein I0 and 5! indicate the prisms disposedbetween the oculars 29 and 3?) and the objectives '3! 211C132 of themicroscope. Each of the objectives 53;! and 32 are angularly disposed toeach other to focus on an object held by a suitable stage (not shown).To deviate the respective beams shown as axially traversing theobjectives so that the emergent'beams will issue parallel to'the roofedges of the prisms-andaxially of the parallel oculars 29 and ill, wedgeprisms and 3 are cemented to the lower innerfaces or" the prisms l8 andI I, one of the isosceles faces of the wedge prisms being cemented tothe face of the prisms it! and H and the other face being disposed at anangle greater than the critical angle to the beam of light'transmittedthrough the objective. The outer facesof wedge prisms 33 and iii-arecoated with opaque layers of reflecting material, indicated at 33' and'34. Such reby the reflecting layer 8- of the wedge .prism 33 tothe roofof the prism l I. he beam viszthen reflected by the roof to'th e upperinner'face of the prism I IJ' from whence-it is-reflectedito the ocular'29 bythe-reflecting layer 3 I55 In likeimanwedge prisms 33 'ment thewedge prisms cre'ased brilliance of light losses. As the path of therays is of considrays incident on an entrance her, the beam of lightfrom the objective 32 is re.- 'flected by the reflecting layer ble toform the roof prisms I9 and l I and the I and 34 separately and then ee-33 and 34 to the lower innerfacesof the prisms l and l l, respectively,

eachof the composite elements of the system,

comprising a roof prism and a wedge prism, may

:be formed of a single piece of glass having their effective facesground so that geometrically speaking they are the same and functionallyequivalent to those of the system shown in Fig. 4.

It 'will be apparent that binocular microscopes embodying the prismaticreversing system of the present invention will stereoscopically enablethe observer to form a magnified three-dimensional picture of the objectspace. As a result, the microscopes permit long periods of observationwith vlittlefatigue and give' a stereoscopic image extremely useful inexamining many objects.

It will be observed that in the embodiments of the prismatic reversingsystem shown in Figs. 2, 3, and 4, several structural and operativeadvantages are gained. The number of air-to-glass facesare reduced to aminimum, insuring the in- V the images by decreasing erable length fromthe objectives to the oculars, lenses of long focal length may beemployed to insure a high degree of magnification without distortion ofthe image. As the prism system com- A prises only two mutuallycooperating prisms having a minimum number of eight faces to beaccurately finished to obtain a complete reversal of the images, theprism system may be economically manufactured. Also, as the prisms maybe readily located and held in an easily formed instrument body, furthersavings are realized in the manufacturing costs of prismaticinstruments.

From the foregoing, it will be apparent that I i am able to attain theobjects of my invention and provide a new and improved prismaticreversing system for prismatic instruments which is efficient inoperation and relatively simple and inexpensive to manufacture. Variousmodifications can, of course, be made without departing from the spiritof my invention or the scope of the appended claims.

I claim:

1. A prismatic reversing system comprising a pair of spaced, oppositelypositioned roof prisms each having a roof portion comprising mutuallycooperating reflecting faces for reversing similar images, each of saidprisms having entrance and exit faces angularly disposed relative toeach other and to the roof of an opposed prism, said prisms beingpositioned with their entrance and exit faces in opposed relation sothat incoming light face of either of the prisms are reflected to theroof of the other prism and reflected by the last-named roof to the exitpair of spaced, oppositely positioned roof prisms each having a roofportion comprising mutually cooperating reflecting faces for reversingsimilar images, each of said prisms having entrance and exit facesangularly disposed relative to each other and to the roof of an opposedprism, said prisms being positioned with their entrance and exit facesin opposed relation so that incoming light rays incident on an entranceface of either of the prisms are reflected to the roof of the otherprism and reflected by the last-named roof to the exit face of thefirst-named prism, said last-named face reflecting the light outwardlyof-the prism system, the remotely positioned portions of the entranceand exit faces of each prism carrying opaque reflecting layers forincreasing the reflectivity of such portions of the faces.

3. A binocular instrument comprising two objectives, two oculars havingtheir axes parallel with the axes of said objectives, and a prismaticreversing system disposed between said objectives and said oculars, saidsystem comprising a pair of opposed similar roof prisms of the Amicitype, each prism of the pair having a reflecting face for reflectingincoming light from an objective to the other prism and the latter prismsuccessively reflecting the light received from said firstnamed prismback to the first-named prism, the first-named prism also having asecond reflecting face for reflecting the light outwardly to an ocular.

4. A binocular telescope comprising a pair of objectives, a pair ofoculars having their axes parallel with the axes of said objectives, anda prismatic reversing system, said system comprising a pair of opposedroof prisms of the Amici type disposed between said objectives andoculars, each of said prisms having an entrance face angularly disposedto the axis of an objective for reflecting light received therefrom, aroof disposed parallel to the axes of said objectives and said ocularsfor receiving the reflected light from the entrance face of an opposedprism; and an exit face angularly disposed to the axis of an ocular forreceiving light from the roof of the opposed prism, said exit facereflecting the light to an ocular.

5. A binocular telescope comprising a pair of objectives, a pair ofoculars, a prismatic reversing system disposed between said objectivesand said oculars, said system comprising two spaced and opposed roofprisms of the Amici type, the longitudinal axes of which are parallel toeach other and to the axes of said objective and said oculars, each ofsaid prisms having an entrance face angularly disposed to an objectivefor reflecting light received therefrom; an exit face angularly disposedto an ocular for reflecting light thereto, and a roof receiving lightfrom an entrance face of'an opposed prism and reflecting the light tothe exit face of the opposed prism.

6. A binocular microscope comprising two spaced objectives, two spacedoculars having their axes angularly disposed to the axes of saidobjectives, a prismatic reversing system located between said objectivesand said oculars, said system comprising two spaced, opposed roof prismshaving their longitudinal axes parallel to the axes of said oculars andto each other, each of said prisms having an entrance face angularlydisposed to an objective for reflecting light received therefrom, eachprism having a roof receiving light from the entrance face of an opposedprism and reflecting the light, and an exit face on each prism angularlydisposed to an ocular for reflecting light received from the roof of anopposed prism to an ocular, said prisms being positioned with theirentrance and exit faces in opposed relation.

'7. A binocular microscope comprising two objectives, two oculars havingtheir axes angularly disposed to the axes of the objectives and to eachother, a prismatic reversing system disposed between said oculars andsaid objectives, said system comprising two similar opposed prismshaving their longitudinal axes inclined to each other and to theobjectives and oculars, each of said prisms having an entrance faceangularly disposed to an objective for reflecting incoming lighttherefrom, each prism having an exit face angularly disposed to anocular for reflecting light to the ocular, and each prism having a roofreceiving light reflected from the entrance face of an opposed prism andsuccessively reflecting the light and directing it to the exit face ofthe opposed prism, the prisms being positioned with their entrance andexit faces in opposed relation.

8. A binocular microscope comprising two objectives, two oculars havingtheir axes angularly disposed to the axes of the objectives and to eachother, a prismatic reversing system disposed between said oculars andsaid objectives, said system comprising two similar opposed roof prisms,each of said prisms having a roof facing outwardly and angularlyinclined to each other, each prism having an entrance face angularlydisposed to an objective and receiving light therefrom to reflect thelight to the roof of the opposed prism, and each prism having an exitface angularly disposed to an ocular for reflecting light received fromthe roof of the opposed prism and reflecting the light to an ocular.

9. An optical system comprising a pair of spaced similar prisms, eachprism having upper and lower inclined faces forming equal angles withthe vertical and positioned, respectively, in intersecting planes, eachprism also having internal reflecting faces meeting to form a roofportion, each of said planes intersecting the planes of said reflectingfaces, said prisms being symmetrically positioned with the correspondinginclined faces opposite each other and with the roof portions remotefrom each other, whereby a light ray striking a lower face of the firstprism will be reflected through the lower face of the second prism,thence be successively reflected by the roof portion and directed ontothe upper face of said first prism and thence reflected vertically.

10. An optical system comprising a pair of spaced similar prisms, eachprism having entrance and exit reflecting faces positioned,respectively, in planes which intersect at an angle of substantially120, each prism also having internal reflecting faces meeting to form aroof portion, the planes of the internal reflecting faces intersectingthe first-named planes, said prisms being symmetrically positioned withthe corresponding entrance and exit faces opposite each other and withthe roof portions remote from each other whereby a light ray strikingthe entrance face of the first prism will be reflected to the roofportion of the second prism, then successively reflected by the roofportion of the second prism and directed onto the exit face of the firstprism and thence reflected outwardly from the system.

DONALD T. STREET.

